Inhibiting Browning Process Of Poly (Lactic Acid) And The Synthesis Of Poly (Trimethylene Terephthalate)

This dissertation focused on the problem of product brown stain in the process of synthesis of PLA by direct melt polycondensation. The reaction process was optimized and modified. Ternary composite catalyst was used to synthesize poly?trimethylene terephthalate? by melt polymerization. Main work and conclusions are as follows:Firstly, this dissertation successfully developed a type of titanium tin composite catalyst to solve the problem of product browning in the process of synthesis of PLA by direct melt polycondensation. The components of titanium tin composite catalyst include titanium iso-propylate?Ti[OCH?CH₃?₂]₄?, p-toluenesulfonic acid?TSA?,2,2-dihydroxy propionic acid ?DMPA?,Phosphoric acid?H₃PO₄? and stannous caprylate?Sn?Oct?₂?. The ratio between the catalyst is:mole ratio Ti[OCH?CH₃?₂]₄:TSA:DMPA=1:2:4, and weight ratio Ti[OCH?CH₃?₂]₄: H₃PO₄:Sn?Oct?₂=1:2:2. Synthesis process is as follows:the raw materials is lactic acid with water. Ti[OCH?CH₃?₂]₄ is 0.5% according to the lactic acid. Ti[OCH?CH₃?₂]₄, TSA and DMPA are complexed under 120? for 2 h, the temperature is rise to 150? and the decompression to reduced to 150 Pa and the reaction is performed for 10 h. Then, we add phosphoric acid and stannous caprylate under nitrogen protection. The temperature is rise to 180? and the decompression to reduced to 80 Pa. After reaction for 8 h we can obtain milk white poly?lactic acid? products and the Mw of the products is over 180,000. And we successfully amplified the process to 5 L reaction kettle.Secondly, we studied on the modification of poly?lactic acid? by melt polycondensation. By controlling the backflow of lactide, we obtained the PLA products that its PDI was around 2.5. Compared with the products without optimization, the tensile strength increased by about 15% and the breaking elongation increased by about 8%. Using lignin modified by sulfonic acid for PLA blending modification, the interface bonding force between the materials increased significantly compared with undecorated lignin. The tensile strength of the composite materials increases by about 10% and the breaking elongation increases by about 20% compared with PLA without modification.Finally, in this paper, we used the ternary composite catalyst composed of titanium iso-propylate, p-toluenesulfonic acid,2,2-dihydroxy propionic acid?ratio between the ternary composite catalyst is 1:2:4? for catalytic synthesis of poly?trimethylene terephthalate? by melt polymerization. Intrinsic viscosity of product is 0.98, and the molecular weight of more than 75000. The products reach the level of engineering plastics. we successfully amplified the process to 5 L reaction kettle. Tensile strength of the products is relatively low, but the breaking elongation is very high. The products show excellent toughness.